1. Field of the Invention
The present invention relates to a navigation device that has a route search function of searching for a guidance traveling route connecting a predetermined starting point with a destination and, more specifically, a function of designating an arbitrary road included in a map image in accordance with a user's operation.
2. Description of the Related Art
Generally, vehicle navigation devices are designed to have various functions, such as a map display function of displaying a map image covering a present position of a vehicle and its surroundings on a screen, a route search function of searching a guidance traveling route to the destination or a pass-through location, which is designated by a user, and a route guiding function of guiding the vehicle according to the guidance route obtained by the route search.
Upon performing the route search to the desired destination using the aforesaid route search function, there are cases where the occurrence of an accident or traffic congestion on a specific road has been known in advance. In such cases, a guidance traveling route bypassing the specific road is required by the user. In order to meet such a request, there has been proposed various methods for the route search.
For instance, a first known type of route search method (hereinafter referred to as the “first prior art”) comprises the steps of searching for a guidance traveling route to the destination; displaying a traveling route list which includes the contents of the guidance traveling route, that is, the names of intersections at which the vehicle turns, and the names of roads between the intersections (for example, Route No. of the National Road, and so on); selecting a road to be bypassed from this traveling route list; and performing another route search for a guidance route which bypasses the selected road, to provide a new or revised guidance route.
Further, a second known type of route search method (hereinafter referred to as the “second prior art”) comprises the steps of designating a predetermined area (for example, a rectangular region) including an avoidance road on the map; and searching for a guidance traveling route with all the roads in the predetermined area set as objects not to be searched.
Moreover, a third known method of searching for a guidance traveling route which bypasses a specific road (hereinafter referred to as the “third prior art”) comprises the steps of designating a location to be avoided on a map; setting a road existing near the location as an object to be avoided, to perform a route search.
In addition, a fourth known method of searching for a guidance traveling route which bypasses a prescribed road (hereinafter referred to as the “fourth prior art”) comprises the steps of performing a route search; designating two locations on a guidance traveling route obtained by the route search; setting an interval between the two locations as an object to be avoided, to carry out another route search.
In the navigation device employing the first prior art described above, the avoidance road is selected from the roads which are divided from one another by the intersections where the vehicle turned. Thus, this navigation device has suffered from inflexibility in the selection of the avoidance road. In other words, in a case where a section to be avoided is short, this navigation device cannot select and bypass this section only, and probably selects a road which has a longer distance than required as the avoidance road, thereby failing to set the avoidance road or section with high accuracy.
Similarly, the navigation device employing the second prior art described above sets all the roads included in the predetermined area as the avoidance roads or sections. Even in a case where only a few roads are to be avoided, more roads than necessary are probably selected to be bypassed, thus making it impossible to set the avoidance road or section accurately.
In the navigation device employing the above-mentioned third prior art, the road near the designated location is specified by a predetermined unit as the avoidance road. The range of the predetermined unit as the avoidance road is difficult for the user to understand, resulting in a disadvantage that the avoidance road cannot be defined in accordance with the user's intention with high accuracy.
The navigation device employing the above-mentioned fourth prior art is designed to designate an avoidance road after displaying a map image with a wide display area including an overall guidance traveling route. In order to designate the avoidance road to a detailed degree, the user must adjust a reduced scale and a display area of the map image so as to display the map image including the avoidance road in the optimal reduced scale. This adjustment involves complicated operation.
The present invention has been accomplished in view of the above-mentioned technical background, and it is an object of the present invention to provide a navigation device that can easily designate the road to be avoided with high accuracy.